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Water quality, pollution and treatment units

Water Quality, Pollution,
and Treatment Plants


Objectives
• Introduce water quality standards
• Introduce typical treatment processes and
design flow rates
• Present examples of flow sheet diagrams


Water Usage
 Domestic
 Industrial
 Agriculture
 Fish farming
 Recreational


Pollution
Pollution


Physical
Physical
Radiological
Radiological

•Thermal
•Solids

Chemical
Chemical

Biological
Biological

•Hardness
•Pathogens
•Heavy metals
•Nutrients
•Pesticides
•Oxygen demanding waste
•Volatile organic compounds

•Radio-isotopes


Storm water pollution
Scale formation due to
water hardness

Red tide due to algae contamination


Water Quality
Standards







.A
Standards for
water usage

B.
Discharge or
effluent
standard

.C
Water quality
objective limit

Drinking
Irrigation
Recreational
Industrial











Stream
Sea
Harbor
Lake

Stream
Sea
Harbor
Lake


A. Drinking Water Standard
A1. US Primary Drinking Water MCL in mg/L (partial list)
Inorganic Chemicals
Arsenic

0.05

Mercury

0.002

Barium

2

Nickel

0.1

Cadmium

0.005

Nitrate (as N)

10

Chromium (total)

0.1

Nitrite (as N)

1

Copper

TT

Nitrate + nitrite

10

Fluoride

4

Selenium

0.05

Lead

TT

Thallium

0.002

Asbestos

7×106 fiber /L
Ethylbenzene

0.7

Vinyl chloride

0.002

VOCs
Benzene

0.005

Carbon tetrachloride 0.005


Different countries may have different drinking water standards


A2. Bacteriological limits for drinking water
US EPA states that “bacterial quality criteria for
drinking water from public supplies require not more
than 1 total-coliform/100 ml as the arithmetic mean of all
water samples examined per month, with no more than 4
coliforms/100 ml in any sample if the number of samples
is ≤ 20/month, or no more than 4 per 100 ml in 5% of the
samples if the number of samples exceeds 20 per month.
Bouwer, Groundwater Hydrology, McGraw-Hill, 1978.


Number of samples taken for coliform testing depends on the
population served by the treatment facility


Example
Water samples from the effluent of a water treatment plant of a town
(39,000 people) were analyzed at regular intervals over a month period.
The numbers of coliform/100 ml sample were as shown below:
According to EPA
regulations, are the
number of samples
and effluent bacterial
quality acceptable?
Explain.

.No Count

.No

Count

.No

Count

.No

Count

1

0

11

1

21

0

31

0

2

0

12

0

22

0

32

0

3

1

13

2

23

2

33

2

4

0

14

5

24

4

34

0

5

1

15

2

25

6

35

0

6

2

16

1

26

1

36

0

7

0

17

1

27

0

37

0

8

0

18

0

28

0

38

5

9

1

19

0

29

0

39

0

10

0

20

0

30

0

40

1


Solution
The population is 39,000, so the minimum number of samples should be
40. Since we have 40 samples then the number of samples taken is OK
The arithmetic average of coliform should not be more
than 1. Since the average number of coliform is 0.95
which is less than 1 then this condition is OK
No more than 5% of the samples should have more than 4
. coliform/100ml
Since the number of samples is 40 then no more than 2 samples (5%)
should have more than 4 coliform/100ml. However, there are three
samples (sample # 14, 25, and 38) that have more than 4 coliform/100ml.
So this is a violation of the regulations.


A3. Secondary Standard for Drinking Water
Contaminant

Level

Effects

Al

0.05-0.2 mg/L

Water discoloration

Cl

250 mg/L

Taste, pipe corrosion

Color

15 color units

Aesthetic

Cu

1 mg/L

Taste, porcelain staining

F

2 mg/L

Dental fluorosis

Foaming agents

0.5 mg/L

Aesthetic

Fe

0.3 mg/L

Taste, laundry staining

pH

6.5-8.5

Corrosive

Sulfate

250 mg/L

Taste, laxative effects


B. Effluent Standards
B1. US National Pollutant Discharge Elimination System
)(NPDES
7 consecutive
days

30 consecutive
days

BOD

45 mg/l

30 mg/l

SS

45 mg/l

30 mg/l

Oil and grease

20 mg/l

10 mg/l

pH: 6-9
BOD and SS removal > 85%


B2. Discharge standard of wastewater into Jebel Ali Harbor
Parameter

Unit

Maximum limit

Total Suspended solids

mg/l

50

-

6-9

C

< 35

BOD

mg/l

50

Dissolved Oxygen

mg/l

>3

Nitrate

mg/l

40

Arsenic

mg/l

0.05

Cadmium

mg/l

0.05

Copper

mg/l

0.5

Lead

mg/l

0.1

Mercury

mg/l

0.001

Oil & Grease

mg/l

10

Phenols

mg/l

0.1

Total Organic Carbon

mg/l

75

Cells/100ml

1000

pH
Temperature

Total Coliform

o


C. Water Quality Objective Limits
Jebel Ali Harbor water quality objective limits
Indicator

Standard (mg/l or as noted)

Lead

0.05

Oil and grease

1

Aluminum

0.2

Arsenic

0.01

Cadmium

0.003

Dissolved oxygen

Not less than 5 mg/l or 90% saturation

Mercury

0.001

BOD5

10

Nitrate-N

0.5

Aromatic hydrocarbons

0.001

pH

1 pH unit from background level or 6.5-8.5

Suspended solids

10 (mean), 25 (maximum)

Temperature

2 oC from background level

Total dissolved solids

2% from background level


Typical Treatment of Contaminants
Parameter/Problem

Treatment Process

Large debris (particles)

Screens (Physical)

Settlable solids

Grit chamber (Physical)

Suspended solids

Coagulation (Chemical)/flocculation
(Physical)/Sedimentation (Physical)
Filtration (Physical)

BOD

Biological reactors (Biological)

Heavy metals

Depending on the metal: Sorption (Chemical),
ion exchange (Chemical), or precipitation
(Chemical)

Trace organic
contaminants

Activated carbon (Chemical) or air stripping
(Chemical) if chemicals are volatile in nature

Microorganisms

Disinfection (mainly Chemical)


(Water Treatment Plant (WTP
A WTP consists of processes to remove contaminants present in the water
such that produced water is suitable for drinking.
The design of a WTP depends on (1) the quality of raw water, (2) the quality
of produced water and the (3) capacity of the plant.
The capacity of the plant depends on the design period (15-25 yrs), the
population served, and the per capita water consumption.
A flow sheet for the plant shows the sequence of the processes used:

Raw water

Produced water

influent

Effluent
WTP


(Wastewater Treatment Plant (WWTP
A WWTP consists of processes to remove contaminants present in the
wastewater such that produced water is suitable for discharge or reuse.
The design of a WWTP depends on (1) the characteristics of wastewater, (2)
the desired characteristics of treated wastewater and the (3) capacity of the
plant.
The capacity of the plant depends on the design period (15-25 yrs), the
population served, and the per capita wastewater generation.
A flow sheet for the plant shows the sequence of the processes used:

Wastewater

Treated
wastewater or

Or influent
WWTP

Effluent


Flow Rates: Water Treatment Plants
Design flow rate =per capita water consumption*population at the end
.of design period
Note that the per capita water consumption increases about 10% of the
.percentage increase in population
Example
A small town with a population of 100,000 and a per capita water
consumption of 500 L/d. A water treatment plant is to be built to serve this
town for the coming 10 yrs. Estimate the design flow rate assuming the
.population after 10 yrs is 150,000
Solution
The percent increase in population = (150000-100000)/100000= 50%
Per capita consumption at the end of design period=500(100%
+50%*10%)=525 L/d
Design flow rate = 150,000 * 525 L/d= 78750 m3/d


Flow Rates: Wastewater Treatment Plants
:Minimum flow rate
Important for design of pipes and channels that carry wastewater with
suspended solids. Minimum velocity to keep organic solids in suspension is 0.3
.m/s and to keep silt and sand in suspension is about 0.6 m/s

:Maximum flow rate
This is the peak hourly flow. Such flow is used to determine the hydraulic
capacity of the treatment plant and collection system.

Design flow rate:
Average daily flow at the end of the design period. Usually the average daily
flow is taken as the average over a continuous of 12 months period.
This design flow rate is used to determine organic loading and for sizing all
treatment units.


Flow Sheet Diagram
River Water Treatment Plant
Coagulant

Chlorine
solution

Raw
water

Effluent
Bar
Screen

Traveling Mixing
Screen

Aeration

Flocculation

Settling

Filtration

Carbon bed
Brine

Add Mg
+
Add F

Filter

Bottle water Plant

Ground
Water

Reverses Osmosis
Filters

G.L

W.T
Well

Filter
Ozonation

Bottled
Water


Example Industrial Wastewater Treatment Plant

Influent

Equalization
Tank

Aeration Tank

Settling Chlorination
Tank
Effluent

Air
Return sludge

Dispersed plug-flow activated sludge plant for an industrial wastewater


Removal Efficiency
Q,
Co

Treatment
Unit

Q,
C

Q= flow rate
Co = influent concentration
C = effluent concentration

Removal efficiency = (Co-C)*100/Co
For example if Co is 100 mg/l and C is 10 mg/l then the
. removal efficiency of the treatment unit is 90%



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